changing diff fluid

[bigtruck21]

In my 03, it has 75w90 in the back and 80w90 in the front. Supposedly gm doesn't recomend putting 75w90 in the front. Does anyone know why? Has anyone done so and their truck was ok in 4wd? When changing the back, do you use a gasket or rtv silicone stuff or both? Supposedly when using the silicone you are supposed to wait 15min for skin to build before putting it on and then wait 4 hours before filling? thanks for the help

[Black02Silverado]

I used 75w-90 in my front diff with no problems at all. I also just used the gasket on the back with a little amount of RTV to hold the gasket on the cover, nothing more than enough to hold it in place while I installed the diff cover. That is all I ever do and never had any problems. I did the same thing on my 65 Impala when I installed the Eaton Posi.

 

 

I have talked to a few that have just used RTV but I don't feel comfortable just using it.

[woyster_00z71]

I just changed the diff fluids in both my Silverado and my Tahoe. I used Mobil 1 75W-90 in the rear and Valvoline 80W-90 in the front. No RTV or sealant on the rear gasket. I set the gasket over the cover and then used two of the bolts to hold it in place while I repositioned it on the diff. BTW, the guy at the Chevy parts counter said not to use any sealant when re-installing the gasket. The rear diff took 2.5 quarts and the front took just over 1.5 quarts.

 

Hope this helps,

B.J.

[awdvkd]

I personally always use a gasket, making gaskets with silicone is shade tree mechanics. Spend $5.00 for a tube of silicone instead of a $3.00 gasket. My 2 cents. If you want some thing to hold the gasket in place use 3M weather strip adhesive, it works great for it.

[Bish]

I'm using Mobil 1 in both front and read for over 90K with no problems.

 

If using synthetic, stay away from RTV as the synthetic will eventually break it down and start a leak. I used a gasket with gasket adhesive on the inside and a coating of oil on the cover side. Now when I change fluid, I tap on the cover with a hammer and it falls off and leaves the gasket on the housing. Makes for an easy change.

[robsawatsky]

I'm pretty sure synthetic is OK for the front diff on a 2003. I do know there was a TSB out regarding synthetic lube for older models - not sure what year now - due to some incompatibility, with the breather tube I believe.